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<a href="bandwidth_8hpp.html">Go to the documentation of this file.</a><div class="fragment"><div class="line"><a id="l00001" name="l00001"></a><span class="lineno">    1</span><span class="comment">/* Flow</span></div>
<div class="line"><a id="l00002" name="l00002"></a><span class="lineno">    2</span><span class="comment"> * Copyright 2023 Akamai Technologies, Inc.</span></div>
<div class="line"><a id="l00003" name="l00003"></a><span class="lineno">    3</span><span class="comment"> *</span></div>
<div class="line"><a id="l00004" name="l00004"></a><span class="lineno">    4</span><span class="comment"> * Licensed under the Apache License, Version 2.0 (the</span></div>
<div class="line"><a id="l00005" name="l00005"></a><span class="lineno">    5</span><span class="comment"> * &quot;License&quot;); you may not use this file except in</span></div>
<div class="line"><a id="l00006" name="l00006"></a><span class="lineno">    6</span><span class="comment"> * compliance with the License.  You may obtain a copy</span></div>
<div class="line"><a id="l00007" name="l00007"></a><span class="lineno">    7</span><span class="comment"> * of the License at</span></div>
<div class="line"><a id="l00008" name="l00008"></a><span class="lineno">    8</span><span class="comment"> *</span></div>
<div class="line"><a id="l00009" name="l00009"></a><span class="lineno">    9</span><span class="comment"> *   https://www.apache.org/licenses/LICENSE-2.0</span></div>
<div class="line"><a id="l00010" name="l00010"></a><span class="lineno">   10</span><span class="comment"> *</span></div>
<div class="line"><a id="l00011" name="l00011"></a><span class="lineno">   11</span><span class="comment"> * Unless required by applicable law or agreed to in</span></div>
<div class="line"><a id="l00012" name="l00012"></a><span class="lineno">   12</span><span class="comment"> * writing, software distributed under the License is</span></div>
<div class="line"><a id="l00013" name="l00013"></a><span class="lineno">   13</span><span class="comment"> * distributed on an &quot;AS IS&quot; BASIS, WITHOUT WARRANTIES OR</span></div>
<div class="line"><a id="l00014" name="l00014"></a><span class="lineno">   14</span><span class="comment"> * CONDITIONS OF ANY KIND, either express or implied.</span></div>
<div class="line"><a id="l00015" name="l00015"></a><span class="lineno">   15</span><span class="comment"> * See the License for the specific language governing</span></div>
<div class="line"><a id="l00016" name="l00016"></a><span class="lineno">   16</span><span class="comment"> * permissions and limitations under the License. */</span></div>
<div class="line"><a id="l00017" name="l00017"></a><span class="lineno">   17</span><span class="comment"></span> </div>
<div class="line"><a id="l00018" name="l00018"></a><span class="lineno">   18</span><span class="comment">/// @file</span></div>
<div class="line"><a id="l00019" name="l00019"></a><span class="lineno">   19</span><span class="comment"></span><span class="preprocessor">#pragma once</span></div>
<div class="line"><a id="l00020" name="l00020"></a><span class="lineno">   20</span> </div>
<div class="line"><a id="l00021" name="l00021"></a><span class="lineno">   21</span><span class="preprocessor">#include &quot;<a class="code" href="detail_2net__flow__fwd_8hpp.html">flow/net_flow/detail/net_flow_fwd.hpp</a>&quot;</span></div>
<div class="line"><a id="l00022" name="l00022"></a><span class="lineno">   22</span><span class="preprocessor">#include &quot;<a class="code" href="peer__socket_8hpp.html">flow/net_flow/peer_socket.hpp</a>&quot;</span></div>
<div class="line"><a id="l00023" name="l00023"></a><span class="lineno">   23</span><span class="preprocessor">#include &lt;boost/weak_ptr.hpp&gt;</span></div>
<div class="line"><a id="l00024" name="l00024"></a><span class="lineno">   24</span> </div>
<div class="line"><a id="l00025" name="l00025"></a><span class="lineno">   25</span><span class="keyword">namespace </span><a class="code hl_namespace" href="namespaceflow_1_1net__flow.html">flow::net_flow</a></div>
<div class="line"><a id="l00026" name="l00026"></a><span class="lineno">   26</span>{</div>
<div class="line"><a id="l00027" name="l00027"></a><span class="lineno">   27</span><span class="comment">// Types.</span></div>
<div class="line"><a id="l00028" name="l00028"></a><span class="lineno">   28</span><span class="comment"></span> </div>
<div class="line"><a id="l00029" name="l00029"></a><span class="lineno">   29</span><span class="comment">/**</span></div>
<div class="line"><a id="l00030" name="l00030"></a><span class="lineno">   30</span><span class="comment"> * A per-Peer_socket module that tries to estimate the bandwidth available to the outgoing flow.</span></div>
<div class="line"><a id="l00031" name="l00031"></a><span class="lineno">   31</span><span class="comment"> * That is, it tries to get at the # of bytes per unit time the outgoing empty pipe can support,</span></div>
<div class="line"><a id="l00032" name="l00032"></a><span class="lineno">   32</span><span class="comment"> * minus the # of bytes per unit time being transferred by all other flows in that pipe (NetFlow or</span></div>
<div class="line"><a id="l00033" name="l00033"></a><span class="lineno">   33</span><span class="comment"> * otherwise).  This is useful primarily for certain congestion control strategies (like</span></div>
<div class="line"><a id="l00034" name="l00034"></a><span class="lineno">   34</span><span class="comment"> * Congestion_control_classic_with_bandwidth_est) but may also be good information to make available</span></div>
<div class="line"><a id="l00035" name="l00035"></a><span class="lineno">   35</span><span class="comment"> * to the application layer (e.g., if the user wants to inform a media player what is a suitable bit</span></div>
<div class="line"><a id="l00036" name="l00036"></a><span class="lineno">   36</span><span class="comment"> * rate to avoid rebuffering).  The latter is the reason why Send_bandwidth_estimator is not part of</span></div>
<div class="line"><a id="l00037" name="l00037"></a><span class="lineno">   37</span><span class="comment"> * a congestion control strategy but rather a separate class.</span></div>
<div class="line"><a id="l00038" name="l00038"></a><span class="lineno">   38</span><span class="comment"> *</span></div>
<div class="line"><a id="l00039" name="l00039"></a><span class="lineno">   39</span><span class="comment"> * How can we make this estimate?  As a black box, we care about just one event, `on_acks(N)`, where `N`</span></div>
<div class="line"><a id="l00040" name="l00040"></a><span class="lineno">   40</span><span class="comment"> * is the number of bytes that have been cleanly acknowledged by the receiver.  The `net_flow` engine</span></div>
<div class="line"><a id="l00041" name="l00041"></a><span class="lineno">   41</span><span class="comment"> * should inform this module about each such event.  The running bandwidth estimate is then</span></div>
<div class="line"><a id="l00042" name="l00042"></a><span class="lineno">   42</span><span class="comment"> * available via bandwidth_bytes_per_time().</span></div>
<div class="line"><a id="l00043" name="l00043"></a><span class="lineno">   43</span><span class="comment"> *</span></div>
<div class="line"><a id="l00044" name="l00044"></a><span class="lineno">   44</span><span class="comment"> * ### Object life cycle ###</span></div>
<div class="line"><a id="l00045" name="l00045"></a><span class="lineno">   45</span><span class="comment"> * There is a strict 1-to-1 relationship between one Send_bandwidth_estimator</span></div>
<div class="line"><a id="l00046" name="l00046"></a><span class="lineno">   46</span><span class="comment"> * instance and one Peer_socket.  A Send_bandwidth_estimator is created shortly after Peer_socket</span></div>
<div class="line"><a id="l00047" name="l00047"></a><span class="lineno">   47</span><span class="comment"> * is and is saved inside the latter.  Conversely a pointer to the Peer_socket is stored inside the</span></div>
<div class="line"><a id="l00048" name="l00048"></a><span class="lineno">   48</span><span class="comment"> * Send_bandwidth_estimator (for read-only access to stats such as SRTT).  The containing</span></div>
<div class="line"><a id="l00049" name="l00049"></a><span class="lineno">   49</span><span class="comment"> * Peer_socket must exist at all times while Send_bandwidth_estimator exists.  Informally it&#39;s</span></div>
<div class="line"><a id="l00050" name="l00050"></a><span class="lineno">   50</span><span class="comment"> * recommended that Peer_socket destructor or other method deletes its Send_bandwidth_estimator</span></div>
<div class="line"><a id="l00051" name="l00051"></a><span class="lineno">   51</span><span class="comment"> * instance when it is no longer needed.</span></div>
<div class="line"><a id="l00052" name="l00052"></a><span class="lineno">   52</span><span class="comment"> *</span></div>
<div class="line"><a id="l00053" name="l00053"></a><span class="lineno">   53</span><span class="comment"> * Relationship with outside world:</span></div>
<div class="line"><a id="l00054" name="l00054"></a><span class="lineno">   54</span><span class="comment"> *</span></div>
<div class="line"><a id="l00055" name="l00055"></a><span class="lineno">   55</span><span class="comment"> *   1.  Send_bandwidth_estimator is a black box to Node and Peer_socket code (no</span></div>
<div class="line"><a id="l00056" name="l00056"></a><span class="lineno">   56</span><span class="comment"> *       access to internals; access only to constructors/destructor and API).</span></div>
<div class="line"><a id="l00057" name="l00057"></a><span class="lineno">   57</span><span class="comment"> *   2.  Send_bandwidth_estimator has `const` (!) `friend` access to Peer_socket</span></div>
<div class="line"><a id="l00058" name="l00058"></a><span class="lineno">   58</span><span class="comment"> *       internals.</span></div>
<div class="line"><a id="l00059" name="l00059"></a><span class="lineno">   59</span><span class="comment"> *   3.  The programmer of Send_bandwidth_estimator must assume a certain event</span></div>
<div class="line"><a id="l00060" name="l00060"></a><span class="lineno">   60</span><span class="comment"> *       model to be followed by Node.  This model is to be explicitly explained in the doc headers</span></div>
<div class="line"><a id="l00061" name="l00061"></a><span class="lineno">   61</span><span class="comment"> *       for any `on_...()` methods.  Node must call the `on_...()` methods as soon as it</span></div>
<div class="line"><a id="l00062" name="l00062"></a><span class="lineno">   62</span><span class="comment"> *       detects the appropriate events, and it should aim to detect them as soon as possible after</span></div>
<div class="line"><a id="l00063" name="l00063"></a><span class="lineno">   63</span><span class="comment"> *       they occur.</span></div>
<div class="line"><a id="l00064" name="l00064"></a><span class="lineno">   64</span><span class="comment"> *   4.  The programmer of Send_bandwidth_estimator subclass may assume the existence</span></div>
<div class="line"><a id="l00065" name="l00065"></a><span class="lineno">   65</span><span class="comment"> *       and meaning of certain state of Peer_socket, which she can use to make internal</span></div>
<div class="line"><a id="l00066" name="l00066"></a><span class="lineno">   66</span><span class="comment"> *       computations.  Any such state (i.e., in addition to the on-event calls, and their</span></div>
<div class="line"><a id="l00067" name="l00067"></a><span class="lineno">   67</span><span class="comment"> *       arguments, in (3)) must be explicitly documented in the class or method doc headers.</span></div>
<div class="line"><a id="l00068" name="l00068"></a><span class="lineno">   68</span><span class="comment"> *   5.  Informally, it is assumed that the Node is sending data at a rate close to the available</span></div>
<div class="line"><a id="l00069" name="l00069"></a><span class="lineno">   69</span><span class="comment"> *       capacity of the pipe at all times (and thus the resulting on_acks() events reflect this</span></div>
<div class="line"><a id="l00070" name="l00070"></a><span class="lineno">   70</span><span class="comment"> *       available maximum possible speed).  (Of course this can only be a best effort and cannot be</span></div>
<div class="line"><a id="l00071" name="l00071"></a><span class="lineno">   71</span><span class="comment"> *       guaranteed; indeed Send_bandwidth_estimator itself can help the congestion control</span></div>
<div class="line"><a id="l00072" name="l00072"></a><span class="lineno">   72</span><span class="comment"> *       mechanism in use to maintain a sending rate close to the maximum possible, which in turn</span></div>
<div class="line"><a id="l00073" name="l00073"></a><span class="lineno">   73</span><span class="comment"> *       will feed good acknowledgment samples to Send_bandwidth_estimator.  It sounds like a</span></div>
<div class="line"><a id="l00074" name="l00074"></a><span class="lineno">   74</span><span class="comment"> *       circular technique, but it can work well.)</span></div>
<div class="line"><a id="l00075" name="l00075"></a><span class="lineno">   75</span><span class="comment"> *</span></div>
<div class="line"><a id="l00076" name="l00076"></a><span class="lineno">   76</span><span class="comment"> * Note that the assumption in (5) can also not hold if the sending rate (and thus the rate of</span></div>
<div class="line"><a id="l00077" name="l00077"></a><span class="lineno">   77</span><span class="comment"> * returning acknowledgments) is application-limited; that is the user is not sending data as fast</span></div>
<div class="line"><a id="l00078" name="l00078"></a><span class="lineno">   78</span><span class="comment"> * Node allows, or in particular simply not sending data.  In that case the bandwidth readings may</span></div>
<div class="line"><a id="l00079" name="l00079"></a><span class="lineno">   79</span><span class="comment"> * be inaccurately low (very much so possibly).  Therefore only rely on the results of this class when</span></div>
<div class="line"><a id="l00080" name="l00080"></a><span class="lineno">   80</span><span class="comment"> * not application-limited in this way.</span></div>
<div class="line"><a id="l00081" name="l00081"></a><span class="lineno">   81</span><span class="comment"> *</span></div>
<div class="line"><a id="l00082" name="l00082"></a><span class="lineno">   82</span><span class="comment"> * ### Units ###</span></div>
<div class="line"><a id="l00083" name="l00083"></a><span class="lineno">   83</span><span class="comment"> * bandwidth_bytes_per_time() returns the current bandwidth estimate per unit time U, as an</span></div>
<div class="line"><a id="l00084" name="l00084"></a><span class="lineno">   84</span><span class="comment"> * *integer* number of bytes (rounded down).  What is U?  U is given as `Time_unit(1)`, where</span></div>
<div class="line"><a id="l00085" name="l00085"></a><span class="lineno">   85</span><span class="comment"> * #Time_unit is a public alias of a boost.chrono duration type.  Be careful in any arithmetic done</span></div>
<div class="line"><a id="l00086" name="l00086"></a><span class="lineno">   86</span><span class="comment"> * with the value returned; both overflow and underflow can occur, if one does not take care to</span></div>
<div class="line"><a id="l00087" name="l00087"></a><span class="lineno">   87</span><span class="comment"> * sanity-check the arithmetic.  The justification for the value of the #Time_unit alias is given</span></div>
<div class="line"><a id="l00088" name="l00088"></a><span class="lineno">   88</span><span class="comment"> * in the #Time_unit doc header.</span></div>
<div class="line"><a id="l00089" name="l00089"></a><span class="lineno">   89</span><span class="comment"> *</span></div>
<div class="line"><a id="l00090" name="l00090"></a><span class="lineno">   90</span><span class="comment"> * ### Thread safety ###</span></div>
<div class="line"><a id="l00091" name="l00091"></a><span class="lineno">   91</span><span class="comment"> * Unless stated otherwise, a Congestion_control_strategy object is to be accessed</span></div>
<div class="line"><a id="l00092" name="l00092"></a><span class="lineno">   92</span><span class="comment"> * from the containing Peer_socket&#39;s Node&#39;s thread W only.</span></div>
<div class="line"><a id="l00093" name="l00093"></a><span class="lineno">   93</span><span class="comment"> *</span></div>
<div class="line"><a id="l00094" name="l00094"></a><span class="lineno">   94</span><span class="comment"> * Implementation notes</span></div>
<div class="line"><a id="l00095" name="l00095"></a><span class="lineno">   95</span><span class="comment"> * --------------------</span></div>
<div class="line"><a id="l00096" name="l00096"></a><span class="lineno">   96</span><span class="comment"> *</span></div>
<div class="line"><a id="l00097" name="l00097"></a><span class="lineno">   97</span><span class="comment"> * How do we estimate the available bandwidth?  Basically, we assume the sender -- whenever giving</span></div>
<div class="line"><a id="l00098" name="l00098"></a><span class="lineno">   98</span><span class="comment"> * us on_acks() events -- is sending data at the maximum possible rate.  Therefore, if we divide the</span></div>
<div class="line"><a id="l00099" name="l00099"></a><span class="lineno">   99</span><span class="comment"> * # of bytes reported in acknowledgments by the time period over which we&#39;ve accumulated those</span></div>
<div class="line"><a id="l00100" name="l00100"></a><span class="lineno">  100</span><span class="comment"> * acknowledgments, then we know the available bandwidth over that time period.  Such bandwidth</span></div>
<div class="line"><a id="l00101" name="l00101"></a><span class="lineno">  101</span><span class="comment"> * samples can be blended with past samples using a low-pass filter to get a smoothed bandwidth</span></div>
<div class="line"><a id="l00102" name="l00102"></a><span class="lineno">  102</span><span class="comment"> * estimate.  Of course the question arises: what time period to choose, and what filter to use?  We</span></div>
<div class="line"><a id="l00103" name="l00103"></a><span class="lineno">  103</span><span class="comment"> * use the Westwood+ algorithm that answers these questions.  The basic idea is to maintain a byte</span></div>
<div class="line"><a id="l00104" name="l00104"></a><span class="lineno">  104</span><span class="comment"> * count that starts at 0 at the beginning of the sample period and keeps accumulating as the</span></div>
<div class="line"><a id="l00105" name="l00105"></a><span class="lineno">  105</span><span class="comment"> * acknowledgments come in; once the sample period &gt; SRTT (smoothed round trip time of the socket),</span></div>
<div class="line"><a id="l00106" name="l00106"></a><span class="lineno">  106</span><span class="comment"> * the bytes/time bandwidth sample is taken and added into the running filter; and the new sample</span></div>
<div class="line"><a id="l00107" name="l00107"></a><span class="lineno">  107</span><span class="comment"> * begins with the byte count at 0.  The justification for these choices is given, partially, in the</span></div>
<div class="line"><a id="l00108" name="l00108"></a><span class="lineno">  108</span><span class="comment"> * code and, more completely, in the papers referenced below.</span></div>
<div class="line"><a id="l00109" name="l00109"></a><span class="lineno">  109</span><span class="comment"> *</span></div>
<div class="line"><a id="l00110" name="l00110"></a><span class="lineno">  110</span><span class="comment"> * Why not make this a strategy pattern (like Congestion_control_strategy hierarchy) instead of just</span></div>
<div class="line"><a id="l00111" name="l00111"></a><span class="lineno">  111</span><span class="comment"> * a single class, so that multiple ways of bandwidth estimation can exist?  Because, as far as I</span></div>
<div class="line"><a id="l00112" name="l00112"></a><span class="lineno">  112</span><span class="comment"> * know, Westwood+ is the best available technique, so I don&#39;t see the point of doing anything else.</span></div>
<div class="line"><a id="l00113" name="l00113"></a><span class="lineno">  113</span><span class="comment"> * If that changes, revisit this.</span></div>
<div class="line"><a id="l00114" name="l00114"></a><span class="lineno">  114</span><span class="comment"> *</span></div>
<div class="line"><a id="l00115" name="l00115"></a><span class="lineno">  115</span><span class="comment"> * @todo Look into Google BBR, a recent (as of 2016) state-of-the-art congestion control algorithm that</span></div>
<div class="line"><a id="l00116" name="l00116"></a><span class="lineno">  116</span><span class="comment"> * aims to estimate bandwidth among other things.  Depending on what what one decides, another bandwidth</span></div>
<div class="line"><a id="l00117" name="l00117"></a><span class="lineno">  117</span><span class="comment"> * estimator class could be written.</span></div>
<div class="line"><a id="l00118" name="l00118"></a><span class="lineno">  118</span><span class="comment"> *</span></div>
<div class="line"><a id="l00119" name="l00119"></a><span class="lineno">  119</span><span class="comment"> * @see Linux kernel&#39;s `tcp_westwood.c` for inspiration behind this implementation; the top comment in</span></div>
<div class="line"><a id="l00120" name="l00120"></a><span class="lineno">  120</span><span class="comment"> *      that file also cites the main papers that describe the Westwood+ bandwidth estimator.</span></div>
<div class="line"><a id="l00121" name="l00121"></a><span class="lineno">  121</span><span class="comment"> */</span></div>
<div class="line"><a id="l00122" name="l00122"></a><span class="lineno"><a class="line" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html">  122</a></span><span class="keyword">class </span><a class="code hl_class" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html">Send_bandwidth_estimator</a> :</div>
<div class="line"><a id="l00123" name="l00123"></a><span class="lineno">  123</span>  <span class="keyword">public</span> <a class="code hl_class" href="classflow_1_1log_1_1Log__context.html">log::Log_context</a>,</div>
<div class="line"><a id="l00124" name="l00124"></a><span class="lineno">  124</span>  <span class="keyword">private</span> boost::noncopyable</div>
<div class="line"><a id="l00125" name="l00125"></a><span class="lineno">  125</span>{</div>
<div class="line"><a id="l00126" name="l00126"></a><span class="lineno">  126</span><span class="keyword">public</span>:</div>
<div class="line"><a id="l00127" name="l00127"></a><span class="lineno">  127</span> </div>
<div class="line"><a id="l00128" name="l00128"></a><span class="lineno">  128</span>  <span class="comment">// Types.</span></div>
<div class="line"><a id="l00129" name="l00129"></a><span class="lineno">  129</span><span class="comment"></span> </div>
<div class="line"><a id="l00130" name="l00130"></a><span class="lineno">  130</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00131" name="l00131"></a><span class="lineno">  131</span><span class="comment">   * Type that represents the number of bytes, either as an absolute amount or over some time</span></div>
<div class="line"><a id="l00132" name="l00132"></a><span class="lineno">  132</span><span class="comment">   * period.  To avoid any surprises we set its width explicitly instead of using `size_t`.</span></div>
<div class="line"><a id="l00133" name="l00133"></a><span class="lineno">  133</span><span class="comment">   */</span></div>
<div class="line"><a id="l00134" name="l00134"></a><span class="lineno"><a class="line" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#a40993b2699c5e8ab69dfd56e57ecdd28">  134</a></span>  <span class="keyword">using </span><a class="code hl_typedef" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#a40993b2699c5e8ab69dfd56e57ecdd28">n_bytes_t</a> = uint64_t;</div>
<div class="line"><a id="l00135" name="l00135"></a><span class="lineno">  135</span><span class="comment"></span> </div>
<div class="line"><a id="l00136" name="l00136"></a><span class="lineno">  136</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00137" name="l00137"></a><span class="lineno">  137</span><span class="comment">   * The primary time unit over which this class reports bandwidth.  So when</span></div>
<div class="line"><a id="l00138" name="l00138"></a><span class="lineno">  138</span><span class="comment">   * bandwidth_bytes_per_time() return the number N, that means its bandwidth estimate is N bytes</span></div>
<div class="line"><a id="l00139" name="l00139"></a><span class="lineno">  139</span><span class="comment">   * per `Time_unit(1)` time.</span></div>
<div class="line"><a id="l00140" name="l00140"></a><span class="lineno">  140</span><span class="comment">   *</span></div>
<div class="line"><a id="l00141" name="l00141"></a><span class="lineno">  141</span><span class="comment">   * ### Implementation notes ###</span></div>
<div class="line"><a id="l00142" name="l00142"></a><span class="lineno">  142</span><span class="comment">   * Why choose milliseconds?  There are two conflicting constraints on</span></div>
<div class="line"><a id="l00143" name="l00143"></a><span class="lineno">  143</span><span class="comment">   * #Time_unit.  In the basic bandwidth sample computation, the formula is B = N/D, where N is the</span></div>
<div class="line"><a id="l00144" name="l00144"></a><span class="lineno">  144</span><span class="comment">   * number of bytes acknowledged over time period D, and D is a #Fine_duration.  Note that B is an</span></div>
<div class="line"><a id="l00145" name="l00145"></a><span class="lineno">  145</span><span class="comment">   * integer (#n_bytes_t), as we try to avoid floating-point computations, so the division rounds</span></div>
<div class="line"><a id="l00146" name="l00146"></a><span class="lineno">  146</span><span class="comment">   * down.  #Fine_duration, we can assume, is at least nanoseconds (10^-9 seconds).</span></div>
<div class="line"><a id="l00147" name="l00147"></a><span class="lineno">  147</span><span class="comment">   *</span></div>
<div class="line"><a id="l00148" name="l00148"></a><span class="lineno">  148</span><span class="comment">   * If #Time_unit is something large, like seconds, then in the straightforward B = N/D formula</span></div>
<div class="line"><a id="l00149" name="l00149"></a><span class="lineno">  149</span><span class="comment">   * nanoseconds must first be converted (with integer math only!) to seconds.  This loses a ton of</span></div>
<div class="line"><a id="l00150" name="l00150"></a><span class="lineno">  150</span><span class="comment">   * precision in D, which will typically be something like .001-.2 seconds (up to about an RTT).</span></div>
<div class="line"><a id="l00151" name="l00151"></a><span class="lineno">  151</span><span class="comment">   * That&#39;s clearly unacceptable.  If #Time_unit is something tiny, like nanoseconds, then N/D&#39;s</span></div>
<div class="line"><a id="l00152" name="l00152"></a><span class="lineno">  152</span><span class="comment">   * minimum non-zero value (1) will represent 10^9 bytes per second (all lower bandwidths B</span></div>
<div class="line"><a id="l00153" name="l00153"></a><span class="lineno">  153</span><span class="comment">   * rounding down to zero), which is clearly absurd.  What about milliseconds?  RTTs are</span></div>
<div class="line"><a id="l00154" name="l00154"></a><span class="lineno">  154</span><span class="comment">   * classically given in milliseconds anyway, so the precision is acceptable (though #Fine_clock can</span></div>
<div class="line"><a id="l00155" name="l00155"></a><span class="lineno">  155</span><span class="comment">   * in fact give much more precise values -- but that precision is not necessary here).  Meanwhile,</span></div>
<div class="line"><a id="l00156" name="l00156"></a><span class="lineno">  156</span><span class="comment">   * the lowest value B = N/D = 1 represents 1000 bytes per second, which is definitely a very low</span></div>
<div class="line"><a id="l00157" name="l00157"></a><span class="lineno">  157</span><span class="comment">   * bandwidth and thus good enough.  So, we use milliseconds.</span></div>
<div class="line"><a id="l00158" name="l00158"></a><span class="lineno">  158</span><span class="comment">   *</span></div>
<div class="line"><a id="l00159" name="l00159"></a><span class="lineno">  159</span><span class="comment">   * Another important reason milliseconds is a reasonable unit is in the outside CWND = B * RTTmin</span></div>
<div class="line"><a id="l00160" name="l00160"></a><span class="lineno">  160</span><span class="comment">   * calculation (see Congestion_control_classic_with_bandwidth_est), where CWND is the congestion</span></div>
<div class="line"><a id="l00161" name="l00161"></a><span class="lineno">  161</span><span class="comment">   * window, B is the bandwidth estimate we generate, and RTTmin is some RTT.  Assuming RTTmin is</span></div>
<div class="line"><a id="l00162" name="l00162"></a><span class="lineno">  162</span><span class="comment">   * also in units of #Time_unit, and we use a very large unit for B, then the result of that</span></div>
<div class="line"><a id="l00163" name="l00163"></a><span class="lineno">  163</span><span class="comment">   * calculation may actually exceed 64 bits, which will cause overflow.  On the other hand if we</span></div>
<div class="line"><a id="l00164" name="l00164"></a><span class="lineno">  164</span><span class="comment">   * just express B in bytes/ms and RTTmin in ms, then the formula avoids that danger while being</span></div>
<div class="line"><a id="l00165" name="l00165"></a><span class="lineno">  165</span><span class="comment">   * quite precise enough.</span></div>
<div class="line"><a id="l00166" name="l00166"></a><span class="lineno">  166</span><span class="comment">   */</span></div>
<div class="line"><a id="l00167" name="l00167"></a><span class="lineno"><a class="line" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#a1e5e59588c6683d56866e49e5fd2980e">  167</a></span>  <span class="keyword">using </span><a class="code hl_typedef" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#a1e5e59588c6683d56866e49e5fd2980e">Time_unit</a> = boost::chrono::milliseconds;</div>
<div class="line"><a id="l00168" name="l00168"></a><span class="lineno">  168</span> </div>
<div class="line"><a id="l00169" name="l00169"></a><span class="lineno">  169</span>  <span class="comment">// Constructors/destructor.</span></div>
<div class="line"><a id="l00170" name="l00170"></a><span class="lineno">  170</span><span class="comment"></span> </div>
<div class="line"><a id="l00171" name="l00171"></a><span class="lineno">  171</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00172" name="l00172"></a><span class="lineno">  172</span><span class="comment">   * Constructs object by setting up logging and saving a pointer to the containing Peer_socket.</span></div>
<div class="line"><a id="l00173" name="l00173"></a><span class="lineno">  173</span><span class="comment">   * bandwidth_bytes_per_time() will return 0 until enough on_acks() events have occurred to make it</span></div>
<div class="line"><a id="l00174" name="l00174"></a><span class="lineno">  174</span><span class="comment">   * receive a higher value, but certainly at least until on_acks() is called once.</span></div>
<div class="line"><a id="l00175" name="l00175"></a><span class="lineno">  175</span><span class="comment">   *</span></div>
<div class="line"><a id="l00176" name="l00176"></a><span class="lineno">  176</span><span class="comment">   * Only a weak pointer of `sock` is stored: the `shared_ptr` itself is not saved, so the reference</span></div>
<div class="line"><a id="l00177" name="l00177"></a><span class="lineno">  177</span><span class="comment">   * count of `sock` does not increase.  This avoids a circular `shared_ptr` situation that would arise</span></div>
<div class="line"><a id="l00178" name="l00178"></a><span class="lineno">  178</span><span class="comment">   * from `*this` pointing to `sock`, and `sock` pointing to `*this` (the two objects *do* need access</span></div>
<div class="line"><a id="l00179" name="l00179"></a><span class="lineno">  179</span><span class="comment">   * to each other, as explained in class doc header).</span></div>
<div class="line"><a id="l00180" name="l00180"></a><span class="lineno">  180</span><span class="comment">   *</span></div>
<div class="line"><a id="l00181" name="l00181"></a><span class="lineno">  181</span><span class="comment">   * @param logger_ptr</span></div>
<div class="line"><a id="l00182" name="l00182"></a><span class="lineno">  182</span><span class="comment">   *        The Logger implementation to use subsequently.</span></div>
<div class="line"><a id="l00183" name="l00183"></a><span class="lineno">  183</span><span class="comment">   * @param sock</span></div>
<div class="line"><a id="l00184" name="l00184"></a><span class="lineno">  184</span><span class="comment">   *        The Peer_socket for which this module will estimate available outgoing bandwidth.</span></div>
<div class="line"><a id="l00185" name="l00185"></a><span class="lineno">  185</span><span class="comment">   */</span></div>
<div class="line"><a id="l00186" name="l00186"></a><span class="lineno">  186</span>  <span class="keyword">explicit</span> <a class="code hl_function" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#ad2432d0e20ebfd1b95009e10f10f08be">Send_bandwidth_estimator</a>(<a class="code hl_class" href="classflow_1_1log_1_1Logger.html">log::Logger</a>* logger_ptr, <a class="code hl_typedef" href="classflow_1_1util_1_1Shared__ptr__alias__holder.html#aef7998db71c60eeb5d1e3d1a97c14886">Peer_socket::Const_ptr</a> sock);</div>
<div class="line"><a id="l00187" name="l00187"></a><span class="lineno">  187</span> </div>
<div class="line"><a id="l00188" name="l00188"></a><span class="lineno">  188</span>  <span class="comment">// Methods.</span></div>
<div class="line"><a id="l00189" name="l00189"></a><span class="lineno">  189</span><span class="comment"></span> </div>
<div class="line"><a id="l00190" name="l00190"></a><span class="lineno">  190</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00191" name="l00191"></a><span class="lineno">  191</span><span class="comment">   * Returns the current estimate of the available outgoing bandwidth per unit time for the</span></div>
<div class="line"><a id="l00192" name="l00192"></a><span class="lineno">  192</span><span class="comment">   * containing socket&#39;s connection, in units of bytes per `Time_unit(1)`.  This value may be zero if</span></div>
<div class="line"><a id="l00193" name="l00193"></a><span class="lineno">  193</span><span class="comment">   * either there is not enough information to make a reasonable estimate, or if the estimated</span></div>
<div class="line"><a id="l00194" name="l00194"></a><span class="lineno">  194</span><span class="comment">   * bandwidth is less than a certain low threshold.</span></div>
<div class="line"><a id="l00195" name="l00195"></a><span class="lineno">  195</span><span class="comment">   *</span></div>
<div class="line"><a id="l00196" name="l00196"></a><span class="lineno">  196</span><span class="comment">   * @return Ditto.</span></div>
<div class="line"><a id="l00197" name="l00197"></a><span class="lineno">  197</span><span class="comment">   */</span></div>
<div class="line"><a id="l00198" name="l00198"></a><span class="lineno">  198</span>  <a class="code hl_typedef" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#a40993b2699c5e8ab69dfd56e57ecdd28">n_bytes_t</a> <a class="code hl_function" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#a135f0a46b34063e10abfb16de057cbb3">bandwidth_bytes_per_time</a>() <span class="keyword">const</span>;</div>
<div class="line"><a id="l00199" name="l00199"></a><span class="lineno">  199</span><span class="comment"></span> </div>
<div class="line"><a id="l00200" name="l00200"></a><span class="lineno">  200</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00201" name="l00201"></a><span class="lineno">  201</span><span class="comment">   * Informs the bandwidth estimator strategy that 1 or more previously sent packets whose status</span></div>
<div class="line"><a id="l00202" name="l00202"></a><span class="lineno">  202</span><span class="comment">   * was In-flight just received acknowledgments, thus changing their state from In-flight to</span></div>
<div class="line"><a id="l00203" name="l00203"></a><span class="lineno">  203</span><span class="comment">   * Acknowledged.  For efficiency and simplicity of behavior, on_acks() should be called as few</span></div>
<div class="line"><a id="l00204" name="l00204"></a><span class="lineno">  204</span><span class="comment">   * times as possible while still satisfying the requirement in the previous sentence.  That is,</span></div>
<div class="line"><a id="l00205" name="l00205"></a><span class="lineno">  205</span><span class="comment">   * suppose acknowledgments for N packets were received simultaneously.  Then on_acks() must be</span></div>
<div class="line"><a id="l00206" name="l00206"></a><span class="lineno">  206</span><span class="comment">   * called one time, not several times.</span></div>
<div class="line"><a id="l00207" name="l00207"></a><span class="lineno">  207</span><span class="comment">   *</span></div>
<div class="line"><a id="l00208" name="l00208"></a><span class="lineno">  208</span><span class="comment">   * on_acks() must be called *after* any RTT measurement based on the acked bytes has affected</span></div>
<div class="line"><a id="l00209" name="l00209"></a><span class="lineno">  209</span><span class="comment">   * the recorded SRTT in `sock` passed in constructor.</span></div>
<div class="line"><a id="l00210" name="l00210"></a><span class="lineno">  210</span><span class="comment">   *</span></div>
<div class="line"><a id="l00211" name="l00211"></a><span class="lineno">  211</span><span class="comment">   * Additional Peer_socket state used: Peer_socket::m_snd_smoothed_round_trip_time.</span></div>
<div class="line"><a id="l00212" name="l00212"></a><span class="lineno">  212</span><span class="comment">   *</span></div>
<div class="line"><a id="l00213" name="l00213"></a><span class="lineno">  213</span><span class="comment">   * Assumptions about ACK sender (DATA received): Same as Congestion_control_strategy::on_acks().</span></div>
<div class="line"><a id="l00214" name="l00214"></a><span class="lineno">  214</span><span class="comment">   * However Send_bandwidth_estimator does not strictly rely on those exact requirements; however it</span></div>
<div class="line"><a id="l00215" name="l00215"></a><span class="lineno">  215</span><span class="comment">   * generally expects quick acknowledgments in order to be effective, and</span></div>
<div class="line"><a id="l00216" name="l00216"></a><span class="lineno">  216</span><span class="comment">   * Congestion_control_strategy::on_acks()&#39;s specific requirements happen to basically satisfy that</span></div>
<div class="line"><a id="l00217" name="l00217"></a><span class="lineno">  217</span><span class="comment">   * informal requirement.</span></div>
<div class="line"><a id="l00218" name="l00218"></a><span class="lineno">  218</span><span class="comment">   *</span></div>
<div class="line"><a id="l00219" name="l00219"></a><span class="lineno">  219</span><span class="comment">   * @note bandwidth_bytes_per_time() may return a different value after this call.  If something,</span></div>
<div class="line"><a id="l00220" name="l00220"></a><span class="lineno">  220</span><span class="comment">   *       like congestion control, relies on that value and can be reasonably be called right after</span></div>
<div class="line"><a id="l00221" name="l00221"></a><span class="lineno">  221</span><span class="comment">   *       or right before this on_acks(), recommend calling it right after this on_acks().</span></div>
<div class="line"><a id="l00222" name="l00222"></a><span class="lineno">  222</span><span class="comment">   * @note Acknowledgments of data that are not currently In-flight due to being Dropped (a/k/a late</span></div>
<div class="line"><a id="l00223" name="l00223"></a><span class="lineno">  223</span><span class="comment">   *       ACKs) or Acknowledged (i.e., duplicate ACKs) must NOT be passed to this method.</span></div>
<div class="line"><a id="l00224" name="l00224"></a><span class="lineno">  224</span><span class="comment">   * @note on_acks() makes no assumptions about how the reported individual packet acks were</span></div>
<div class="line"><a id="l00225" name="l00225"></a><span class="lineno">  225</span><span class="comment">   *       packaged by the ACK sender into actual ACK packets (how many ACKs there were, etc.).</span></div>
<div class="line"><a id="l00226" name="l00226"></a><span class="lineno">  226</span><span class="comment">   *       It just assumes every individual acknowledgment is reported to on_acks() as soon as</span></div>
<div class="line"><a id="l00227" name="l00227"></a><span class="lineno">  227</span><span class="comment">   *       possible and grouped into as few on_acks() calls as possible.</span></div>
<div class="line"><a id="l00228" name="l00228"></a><span class="lineno">  228</span><span class="comment">   * @note For definition of In-flight, Acknowledged, and Dropped bytes, see</span></div>
<div class="line"><a id="l00229" name="l00229"></a><span class="lineno">  229</span><span class="comment">   *       Peer_socket::m_snd_flying_pkts_by_sent_when and Peer_socket::m_snd_flying_pkts_by_seq_num.</span></div>
<div class="line"><a id="l00230" name="l00230"></a><span class="lineno">  230</span><span class="comment">   *</span></div>
<div class="line"><a id="l00231" name="l00231"></a><span class="lineno">  231</span><span class="comment">   * @param bytes</span></div>
<div class="line"><a id="l00232" name="l00232"></a><span class="lineno">  232</span><span class="comment">   *        The sum of the number of bytes in the user data fields of the packets that have been</span></div>
<div class="line"><a id="l00233" name="l00233"></a><span class="lineno">  233</span><span class="comment">   *        Acknowledged.  Must not be zero.</span></div>
<div class="line"><a id="l00234" name="l00234"></a><span class="lineno">  234</span><span class="comment">   */</span></div>
<div class="line"><a id="l00235" name="l00235"></a><span class="lineno">  235</span>  <span class="keywordtype">void</span> <a class="code hl_function" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#afe271b3d4c8cb73d06048a41871c795e">on_acks</a>(<span class="keywordtype">size_t</span> bytes);</div>
<div class="line"><a id="l00236" name="l00236"></a><span class="lineno">  236</span> </div>
<div class="line"><a id="l00237" name="l00237"></a><span class="lineno">  237</span><span class="keyword">private</span>:</div>
<div class="line"><a id="l00238" name="l00238"></a><span class="lineno">  238</span>  <span class="comment">// Methods.</span></div>
<div class="line"><a id="l00239" name="l00239"></a><span class="lineno">  239</span><span class="comment"></span> </div>
<div class="line"><a id="l00240" name="l00240"></a><span class="lineno">  240</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00241" name="l00241"></a><span class="lineno">  241</span><span class="comment">   * Applies the low-pass filter that takes the given previous result of the filter and blends in</span></div>
<div class="line"><a id="l00242" name="l00242"></a><span class="lineno">  242</span><span class="comment">   * the given new sample.  The values should be in the same units, which are presumably bytes per</span></div>
<div class="line"><a id="l00243" name="l00243"></a><span class="lineno">  243</span><span class="comment">   * `Time_unit(1)`.</span></div>
<div class="line"><a id="l00244" name="l00244"></a><span class="lineno">  244</span><span class="comment">   *</span></div>
<div class="line"><a id="l00245" name="l00245"></a><span class="lineno">  245</span><span class="comment">   * @param prev_val_per_time</span></div>
<div class="line"><a id="l00246" name="l00246"></a><span class="lineno">  246</span><span class="comment">   *        Previous result of this filter.</span></div>
<div class="line"><a id="l00247" name="l00247"></a><span class="lineno">  247</span><span class="comment">   * @param new_sample_val_per_time</span></div>
<div class="line"><a id="l00248" name="l00248"></a><span class="lineno">  248</span><span class="comment">   *        New sample to blend into that filter.</span></div>
<div class="line"><a id="l00249" name="l00249"></a><span class="lineno">  249</span><span class="comment">   * @return The blended value.</span></div>
<div class="line"><a id="l00250" name="l00250"></a><span class="lineno">  250</span><span class="comment">   */</span></div>
<div class="line"><a id="l00251" name="l00251"></a><span class="lineno">  251</span>  <span class="keyword">static</span> <a class="code hl_typedef" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#a40993b2699c5e8ab69dfd56e57ecdd28">n_bytes_t</a> <a class="code hl_function" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#a2d19118df3aa42de866343893dc75a0a">apply_filter</a>(<a class="code hl_typedef" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#a40993b2699c5e8ab69dfd56e57ecdd28">n_bytes_t</a> prev_val_per_time, <a class="code hl_typedef" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#a40993b2699c5e8ab69dfd56e57ecdd28">n_bytes_t</a> new_sample_val_per_time);</div>
<div class="line"><a id="l00252" name="l00252"></a><span class="lineno">  252</span><span class="comment"></span> </div>
<div class="line"><a id="l00253" name="l00253"></a><span class="lineno">  253</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00254" name="l00254"></a><span class="lineno">  254</span><span class="comment">   * Utility that returns a handle to the containing Peer_socket.  If somehow the containing</span></div>
<div class="line"><a id="l00255" name="l00255"></a><span class="lineno">  255</span><span class="comment">   * Peer_socket has been deleted, `assert()` trips.</span></div>
<div class="line"><a id="l00256" name="l00256"></a><span class="lineno">  256</span><span class="comment">   *</span></div>
<div class="line"><a id="l00257" name="l00257"></a><span class="lineno">  257</span><span class="comment">   * @return Ditto.</span></div>
<div class="line"><a id="l00258" name="l00258"></a><span class="lineno">  258</span><span class="comment">   */</span></div>
<div class="line"><a id="l00259" name="l00259"></a><span class="lineno">  259</span>  <a class="code hl_typedef" href="classflow_1_1util_1_1Shared__ptr__alias__holder.html#aef7998db71c60eeb5d1e3d1a97c14886">Peer_socket::Const_ptr</a> <a class="code hl_function" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#a8676142f693c447be89b667403fecea1">socket</a>() <span class="keyword">const</span>;</div>
<div class="line"><a id="l00260" name="l00260"></a><span class="lineno">  260</span> </div>
<div class="line"><a id="l00261" name="l00261"></a><span class="lineno">  261</span>  <span class="comment">// Data.</span></div>
<div class="line"><a id="l00262" name="l00262"></a><span class="lineno">  262</span><span class="comment"></span> </div>
<div class="line"><a id="l00263" name="l00263"></a><span class="lineno">  263</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00264" name="l00264"></a><span class="lineno">  264</span><span class="comment">   * The containing socket (read-only access).  Implementation may rely on various state stored</span></div>
<div class="line"><a id="l00265" name="l00265"></a><span class="lineno">  265</span><span class="comment">   * inside the pointed-to Peer_socket.</span></div>
<div class="line"><a id="l00266" name="l00266"></a><span class="lineno">  266</span><span class="comment">   *</span></div>
<div class="line"><a id="l00267" name="l00267"></a><span class="lineno">  267</span><span class="comment">   * Why `weak_ptr`?  See similar comment on Congestion_control_strategy::m_sock.</span></div>
<div class="line"><a id="l00268" name="l00268"></a><span class="lineno">  268</span><span class="comment">   */</span></div>
<div class="line"><a id="l00269" name="l00269"></a><span class="lineno"><a class="line" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#a380927913e47235684ce014b14371920">  269</a></span>  boost::weak_ptr&lt;Peer_socket::Const_ptr::element_type&gt; <a class="code hl_variable" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#a380927913e47235684ce014b14371920">m_sock</a>;</div>
<div class="line"><a id="l00270" name="l00270"></a><span class="lineno">  270</span><span class="comment"></span> </div>
<div class="line"><a id="l00271" name="l00271"></a><span class="lineno">  271</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00272" name="l00272"></a><span class="lineno">  272</span><span class="comment">   * The current smoothed bandwidth estimate, to be returned by bandwidth_bytes_per_time(), in the</span></div>
<div class="line"><a id="l00273" name="l00273"></a><span class="lineno">  273</span><span class="comment">   * units described by that method&#39;s doc header.  Zero until the first sample is completed.</span></div>
<div class="line"><a id="l00274" name="l00274"></a><span class="lineno">  274</span><span class="comment">   */</span></div>
<div class="line"><a id="l00275" name="l00275"></a><span class="lineno"><a class="line" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#aee344345b4b4c54a0854bfd23817ef46">  275</a></span>  <a class="code hl_typedef" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#a40993b2699c5e8ab69dfd56e57ecdd28">n_bytes_t</a> <a class="code hl_variable" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#aee344345b4b4c54a0854bfd23817ef46">m_bytes_per_time_smoothed</a>;</div>
<div class="line"><a id="l00276" name="l00276"></a><span class="lineno">  276</span><span class="comment"></span> </div>
<div class="line"><a id="l00277" name="l00277"></a><span class="lineno">  277</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00278" name="l00278"></a><span class="lineno">  278</span><span class="comment">   * In the same units as #m_bytes_per_time_smoothed, the less smoothed bandwidth estimate, which is</span></div>
<div class="line"><a id="l00279" name="l00279"></a><span class="lineno">  279</span><span class="comment">   * simply the progressive application of apply_filter() on each available bandwidth sample.  It&#39;s</span></div>
<div class="line"><a id="l00280" name="l00280"></a><span class="lineno">  280</span><span class="comment">   * not used by bandwidth_bytes_per_time() but instead is blended into #m_bytes_per_time_smoothed.</span></div>
<div class="line"><a id="l00281" name="l00281"></a><span class="lineno">  281</span><span class="comment">   *</span></div>
<div class="line"><a id="l00282" name="l00282"></a><span class="lineno">  282</span><span class="comment">   * I do not really understand why `tcp_westwood.c` (Linux kernel) does it that way; I get that it</span></div>
<div class="line"><a id="l00283" name="l00283"></a><span class="lineno">  283</span><span class="comment">   * adds an extra level of smoothing, but I did not catch any obvious references to this in the</span></div>
<div class="line"><a id="l00284" name="l00284"></a><span class="lineno">  284</span><span class="comment">   * papers.  Perhaps this is some elementary math that is just assumed to be understood.  Anyway, I</span></div>
<div class="line"><a id="l00285" name="l00285"></a><span class="lineno">  285</span><span class="comment">   * took it from `tcp_westwood.c`.  Their comment on the equivalent data member `bw_ns_est` says:</span></div>
<div class="line"><a id="l00286" name="l00286"></a><span class="lineno">  286</span><span class="comment">   * &quot;first bandwidth estimation..not too smoothed 8)&quot; which is not too helpful to me.</span></div>
<div class="line"><a id="l00287" name="l00287"></a><span class="lineno">  287</span><span class="comment">   */</span></div>
<div class="line"><a id="l00288" name="l00288"></a><span class="lineno"><a class="line" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#ae6e40f0e24775a09a60dcb7d18242a02">  288</a></span>  <a class="code hl_typedef" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#a40993b2699c5e8ab69dfd56e57ecdd28">n_bytes_t</a> <a class="code hl_variable" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#ae6e40f0e24775a09a60dcb7d18242a02">m_bytes_per_time_less_smoothed</a>;</div>
<div class="line"><a id="l00289" name="l00289"></a><span class="lineno">  289</span><span class="comment"></span> </div>
<div class="line"><a id="l00290" name="l00290"></a><span class="lineno">  290</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00291" name="l00291"></a><span class="lineno">  291</span><span class="comment">   * The number of bytes acknowledged by receiver since #m_this_sample_start_time (the time when the</span></div>
<div class="line"><a id="l00292" name="l00292"></a><span class="lineno">  292</span><span class="comment">   * current sample began to be compiled).  When a sample is deemed sufficient, `m_bytes_this_sample</span></div>
<div class="line"><a id="l00293" name="l00293"></a><span class="lineno">  293</span><span class="comment">   * / (now() - m_this_sample_start_time)` is the individual bandwidth sample fed into the filter.</span></div>
<div class="line"><a id="l00294" name="l00294"></a><span class="lineno">  294</span><span class="comment">   */</span></div>
<div class="line"><a id="l00295" name="l00295"></a><span class="lineno"><a class="line" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#a0bf439f5cfe98fb1d4d6d55ae605d278">  295</a></span>  <a class="code hl_typedef" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#a40993b2699c5e8ab69dfd56e57ecdd28">n_bytes_t</a> <a class="code hl_variable" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#a0bf439f5cfe98fb1d4d6d55ae605d278">m_bytes_this_sample</a>;</div>
<div class="line"><a id="l00296" name="l00296"></a><span class="lineno">  296</span><span class="comment"></span> </div>
<div class="line"><a id="l00297" name="l00297"></a><span class="lineno">  297</span><span class="comment">  /// The time at which the currently ongoing bandwidth sample began to accumulate.</span></div>
<div class="line"><a id="l00298" name="l00298"></a><span class="lineno"><a class="line" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#ac627f8c9ae6c51c2ea14dd46af4f4150">  298</a></span><span class="comment"></span>  <a class="code hl_typedef" href="namespaceflow.html#a9d9cc2eeb10d398cff5591d446b763b8">Fine_time_pt</a> <a class="code hl_variable" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#ac627f8c9ae6c51c2ea14dd46af4f4150">m_this_sample_start_time</a>;</div>
<div class="line"><a id="l00299" name="l00299"></a><span class="lineno">  299</span><span class="comment"></span> </div>
<div class="line"><a id="l00300" name="l00300"></a><span class="lineno">  300</span><span class="comment">  /// `true` until on_acks() called for the first time; `false` forever thereafter.  Used to begin the sample sequence.</span></div>
<div class="line"><a id="l00301" name="l00301"></a><span class="lineno"><a class="line" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#adc8e7ca2c14f74a85beb863c145b97ba">  301</a></span><span class="comment"></span>  <span class="keywordtype">bool</span> <a class="code hl_variable" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#adc8e7ca2c14f74a85beb863c145b97ba">m_no_acks_yet</a>;</div>
<div class="line"><a id="l00302" name="l00302"></a><span class="lineno">  302</span><span class="comment"></span> </div>
<div class="line"><a id="l00303" name="l00303"></a><span class="lineno">  303</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00304" name="l00304"></a><span class="lineno">  304</span><span class="comment">   * `true` until a sample has been completed and fed into the filter; `false` forever thereafter.  Used to begin the</span></div>
<div class="line"><a id="l00305" name="l00305"></a><span class="lineno">  305</span><span class="comment">   * sample sequence.</span></div>
<div class="line"><a id="l00306" name="l00306"></a><span class="lineno">  306</span><span class="comment">   */</span></div>
<div class="line"><a id="l00307" name="l00307"></a><span class="lineno"><a class="line" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#ac89711897d0c265eb3b18a748c03d3aa">  307</a></span>  <span class="keywordtype">bool</span> <a class="code hl_variable" href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#ac89711897d0c265eb3b18a748c03d3aa">m_no_samples_yet</a>;</div>
<div class="line"><a id="l00308" name="l00308"></a><span class="lineno">  308</span>}; <span class="comment">// class Send_bandwidth_estimator</span></div>
<div class="line"><a id="l00309" name="l00309"></a><span class="lineno">  309</span> </div>
<div class="line"><a id="l00310" name="l00310"></a><span class="lineno">  310</span>} <span class="comment">// namespace flow::net_flow</span></div>
<div class="ttc" id="aclassflow_1_1log_1_1Log__context_html"><div class="ttname"><a href="classflow_1_1log_1_1Log__context.html">flow::log::Log_context</a></div><div class="ttdoc">Convenience class that simply stores a Logger and/or Component passed into a constructor; and returns...</div><div class="ttdef"><b>Definition:</b> <a href="log_8hpp_source.html#l01609">log.hpp:1610</a></div></div>
<div class="ttc" id="aclassflow_1_1log_1_1Logger_html"><div class="ttname"><a href="classflow_1_1log_1_1Logger.html">flow::log::Logger</a></div><div class="ttdoc">Interface that the user should implement, passing the implementing Logger into logging classes (Flow'...</div><div class="ttdef"><b>Definition:</b> <a href="log_8hpp_source.html#l01280">log.hpp:1284</a></div></div>
<div class="ttc" id="aclassflow_1_1net__flow_1_1Send__bandwidth__estimator_html"><div class="ttname"><a href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html">flow::net_flow::Send_bandwidth_estimator</a></div><div class="ttdoc">A per-Peer_socket module that tries to estimate the bandwidth available to the outgoing flow.</div><div class="ttdef"><b>Definition:</b> <a href="bandwidth_8hpp_source.html#l00122">bandwidth.hpp:125</a></div></div>
<div class="ttc" id="aclassflow_1_1net__flow_1_1Send__bandwidth__estimator_html_a0bf439f5cfe98fb1d4d6d55ae605d278"><div class="ttname"><a href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#a0bf439f5cfe98fb1d4d6d55ae605d278">flow::net_flow::Send_bandwidth_estimator::m_bytes_this_sample</a></div><div class="ttdeci">n_bytes_t m_bytes_this_sample</div><div class="ttdoc">The number of bytes acknowledged by receiver since m_this_sample_start_time (the time when the curren...</div><div class="ttdef"><b>Definition:</b> <a href="bandwidth_8hpp_source.html#l00295">bandwidth.hpp:295</a></div></div>
<div class="ttc" id="aclassflow_1_1net__flow_1_1Send__bandwidth__estimator_html_a135f0a46b34063e10abfb16de057cbb3"><div class="ttname"><a href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#a135f0a46b34063e10abfb16de057cbb3">flow::net_flow::Send_bandwidth_estimator::bandwidth_bytes_per_time</a></div><div class="ttdeci">n_bytes_t bandwidth_bytes_per_time() const</div><div class="ttdoc">Returns the current estimate of the available outgoing bandwidth per unit time for the containing soc...</div><div class="ttdef"><b>Definition:</b> <a href="bandwidth_8cpp_source.html#l00038">bandwidth.cpp:38</a></div></div>
<div class="ttc" id="aclassflow_1_1net__flow_1_1Send__bandwidth__estimator_html_a1e5e59588c6683d56866e49e5fd2980e"><div class="ttname"><a href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#a1e5e59588c6683d56866e49e5fd2980e">flow::net_flow::Send_bandwidth_estimator::Time_unit</a></div><div class="ttdeci">boost::chrono::milliseconds Time_unit</div><div class="ttdoc">The primary time unit over which this class reports bandwidth.</div><div class="ttdef"><b>Definition:</b> <a href="bandwidth_8hpp_source.html#l00167">bandwidth.hpp:167</a></div></div>
<div class="ttc" id="aclassflow_1_1net__flow_1_1Send__bandwidth__estimator_html_a2d19118df3aa42de866343893dc75a0a"><div class="ttname"><a href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#a2d19118df3aa42de866343893dc75a0a">flow::net_flow::Send_bandwidth_estimator::apply_filter</a></div><div class="ttdeci">static n_bytes_t apply_filter(n_bytes_t prev_val_per_time, n_bytes_t new_sample_val_per_time)</div><div class="ttdoc">Applies the low-pass filter that takes the given previous result of the filter and blends in the give...</div><div class="ttdef"><b>Definition:</b> <a href="bandwidth_8cpp_source.html#l00231">bandwidth.cpp:231</a></div></div>
<div class="ttc" id="aclassflow_1_1net__flow_1_1Send__bandwidth__estimator_html_a380927913e47235684ce014b14371920"><div class="ttname"><a href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#a380927913e47235684ce014b14371920">flow::net_flow::Send_bandwidth_estimator::m_sock</a></div><div class="ttdeci">boost::weak_ptr&lt; Peer_socket::Const_ptr::element_type &gt; m_sock</div><div class="ttdoc">The containing socket (read-only access).</div><div class="ttdef"><b>Definition:</b> <a href="bandwidth_8hpp_source.html#l00269">bandwidth.hpp:269</a></div></div>
<div class="ttc" id="aclassflow_1_1net__flow_1_1Send__bandwidth__estimator_html_a40993b2699c5e8ab69dfd56e57ecdd28"><div class="ttname"><a href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#a40993b2699c5e8ab69dfd56e57ecdd28">flow::net_flow::Send_bandwidth_estimator::n_bytes_t</a></div><div class="ttdeci">uint64_t n_bytes_t</div><div class="ttdoc">Type that represents the number of bytes, either as an absolute amount or over some time period.</div><div class="ttdef"><b>Definition:</b> <a href="bandwidth_8hpp_source.html#l00134">bandwidth.hpp:134</a></div></div>
<div class="ttc" id="aclassflow_1_1net__flow_1_1Send__bandwidth__estimator_html_a8676142f693c447be89b667403fecea1"><div class="ttname"><a href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#a8676142f693c447be89b667403fecea1">flow::net_flow::Send_bandwidth_estimator::socket</a></div><div class="ttdeci">Peer_socket::Const_ptr socket() const</div><div class="ttdoc">Utility that returns a handle to the containing Peer_socket.</div><div class="ttdef"><b>Definition:</b> <a href="bandwidth_8cpp_source.html#l00238">bandwidth.cpp:238</a></div></div>
<div class="ttc" id="aclassflow_1_1net__flow_1_1Send__bandwidth__estimator_html_ac627f8c9ae6c51c2ea14dd46af4f4150"><div class="ttname"><a href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#ac627f8c9ae6c51c2ea14dd46af4f4150">flow::net_flow::Send_bandwidth_estimator::m_this_sample_start_time</a></div><div class="ttdeci">Fine_time_pt m_this_sample_start_time</div><div class="ttdoc">The time at which the currently ongoing bandwidth sample began to accumulate.</div><div class="ttdef"><b>Definition:</b> <a href="bandwidth_8hpp_source.html#l00298">bandwidth.hpp:298</a></div></div>
<div class="ttc" id="aclassflow_1_1net__flow_1_1Send__bandwidth__estimator_html_ac89711897d0c265eb3b18a748c03d3aa"><div class="ttname"><a href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#ac89711897d0c265eb3b18a748c03d3aa">flow::net_flow::Send_bandwidth_estimator::m_no_samples_yet</a></div><div class="ttdeci">bool m_no_samples_yet</div><div class="ttdoc">true until a sample has been completed and fed into the filter; false forever thereafter.</div><div class="ttdef"><b>Definition:</b> <a href="bandwidth_8hpp_source.html#l00307">bandwidth.hpp:307</a></div></div>
<div class="ttc" id="aclassflow_1_1net__flow_1_1Send__bandwidth__estimator_html_ad2432d0e20ebfd1b95009e10f10f08be"><div class="ttname"><a href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#ad2432d0e20ebfd1b95009e10f10f08be">flow::net_flow::Send_bandwidth_estimator::Send_bandwidth_estimator</a></div><div class="ttdeci">Send_bandwidth_estimator(log::Logger *logger_ptr, Peer_socket::Const_ptr sock)</div><div class="ttdoc">Constructs object by setting up logging and saving a pointer to the containing Peer_socket.</div><div class="ttdef"><b>Definition:</b> <a href="bandwidth_8cpp_source.html#l00026">bandwidth.cpp:26</a></div></div>
<div class="ttc" id="aclassflow_1_1net__flow_1_1Send__bandwidth__estimator_html_adc8e7ca2c14f74a85beb863c145b97ba"><div class="ttname"><a href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#adc8e7ca2c14f74a85beb863c145b97ba">flow::net_flow::Send_bandwidth_estimator::m_no_acks_yet</a></div><div class="ttdeci">bool m_no_acks_yet</div><div class="ttdoc">true until on_acks() called for the first time; false forever thereafter. Used to begin the sample se...</div><div class="ttdef"><b>Definition:</b> <a href="bandwidth_8hpp_source.html#l00301">bandwidth.hpp:301</a></div></div>
<div class="ttc" id="aclassflow_1_1net__flow_1_1Send__bandwidth__estimator_html_ae6e40f0e24775a09a60dcb7d18242a02"><div class="ttname"><a href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#ae6e40f0e24775a09a60dcb7d18242a02">flow::net_flow::Send_bandwidth_estimator::m_bytes_per_time_less_smoothed</a></div><div class="ttdeci">n_bytes_t m_bytes_per_time_less_smoothed</div><div class="ttdoc">In the same units as m_bytes_per_time_smoothed, the less smoothed bandwidth estimate,...</div><div class="ttdef"><b>Definition:</b> <a href="bandwidth_8hpp_source.html#l00288">bandwidth.hpp:288</a></div></div>
<div class="ttc" id="aclassflow_1_1net__flow_1_1Send__bandwidth__estimator_html_aee344345b4b4c54a0854bfd23817ef46"><div class="ttname"><a href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#aee344345b4b4c54a0854bfd23817ef46">flow::net_flow::Send_bandwidth_estimator::m_bytes_per_time_smoothed</a></div><div class="ttdeci">n_bytes_t m_bytes_per_time_smoothed</div><div class="ttdoc">The current smoothed bandwidth estimate, to be returned by bandwidth_bytes_per_time(),...</div><div class="ttdef"><b>Definition:</b> <a href="bandwidth_8hpp_source.html#l00275">bandwidth.hpp:275</a></div></div>
<div class="ttc" id="aclassflow_1_1net__flow_1_1Send__bandwidth__estimator_html_afe271b3d4c8cb73d06048a41871c795e"><div class="ttname"><a href="classflow_1_1net__flow_1_1Send__bandwidth__estimator.html#afe271b3d4c8cb73d06048a41871c795e">flow::net_flow::Send_bandwidth_estimator::on_acks</a></div><div class="ttdeci">void on_acks(size_t bytes)</div><div class="ttdoc">Informs the bandwidth estimator strategy that 1 or more previously sent packets whose status was In-f...</div><div class="ttdef"><b>Definition:</b> <a href="bandwidth_8cpp_source.html#l00043">bandwidth.cpp:43</a></div></div>
<div class="ttc" id="aclassflow_1_1util_1_1Shared__ptr__alias__holder_html_aef7998db71c60eeb5d1e3d1a97c14886"><div class="ttname"><a href="classflow_1_1util_1_1Shared__ptr__alias__holder.html#aef7998db71c60eeb5d1e3d1a97c14886">flow::util::Shared_ptr_alias_holder&lt; boost::shared_ptr&lt; Peer_socket &gt; &gt;::Const_ptr</a></div><div class="ttdeci">Const_target_ptr Const_ptr</div><div class="ttdoc">Short-hand for ref-counted pointer to immutable values of type Target_type::element_type (a-la T cons...</div><div class="ttdef"><b>Definition:</b> <a href="shared__ptr__alias__holder_8hpp_source.html#l00127">shared_ptr_alias_holder.hpp:127</a></div></div>
<div class="ttc" id="adetail_2net__flow__fwd_8hpp_html"><div class="ttname"><a href="detail_2net__flow__fwd_8hpp.html">net_flow_fwd.hpp</a></div></div>
<div class="ttc" id="anamespaceflow_1_1net__flow_html"><div class="ttname"><a href="namespaceflow_1_1net__flow.html">flow::net_flow</a></div><div class="ttdoc">Flow module containing the API and implementation of the Flow network protocol, a TCP-inspired stream...</div><div class="ttdef"><b>Definition:</b> <a href="asio_2node_8cpp_source.html#l00024">node.cpp:25</a></div></div>
<div class="ttc" id="anamespaceflow_html_a9d9cc2eeb10d398cff5591d446b763b8"><div class="ttname"><a href="namespaceflow.html#a9d9cc2eeb10d398cff5591d446b763b8">flow::Fine_time_pt</a></div><div class="ttdeci">Fine_clock::time_point Fine_time_pt</div><div class="ttdoc">A high-res time point as returned by Fine_clock::now() and suitable for precise time math in general.</div><div class="ttdef"><b>Definition:</b> <a href="common_8hpp_source.html#l00413">common.hpp:413</a></div></div>
<div class="ttc" id="apeer__socket_8hpp_html"><div class="ttname"><a href="peer__socket_8hpp.html">peer_socket.hpp</a></div></div>
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